Interaction of Whey Proteins with Phenolic Derivatives Under Neutral and Acidic pH Conditions

Abstract

Integration of gallic acid (GA) and its derivative epigallocatechin gallate (EGCG; 20, 120, and 240 μmol/g, protein basis) into whey protein isolate (WPI) at room temperature and pH 3.0 and pH 7.0 was investigated. At pH 7.0, both phenolics caused significant structural changes and EGCG induced greater digestibility of WPI. Total sulfhydryl in WPI decreased from 28.6 to 7.6 μmol/g and surface hydrophobicity declined by nearly 50% with 240 μmol/g EGCG at pH 7.0. Similar but less appreciable changes were produced by GA and at pH 3.0. Isothermal titration and fluorescence quenching tests showed moderately weak binding of WPI with GA but strong binding with EGCG at pH 7.0. Both phenolics at high concentrations lowered the thermal transition temperature of β-lactoglobulin by 0.5 °C to 1.4 °C and promoted its digestion. The phenolics also displayed a remarkable synergism with peptides in the WPI digest exerting radical scavenging activity.

Covalent Whey Protein–Rosmarinic Acid Interactions: A Comparison of Alkaline and Enzymatic Modifications on Physicochemical, Antioxidative, and Antibacterial Properties

“…Thus, a covalent modification of the proteins amine groups, but even more so with thiol groups, is possible after alkaline modification. These findings are in agreement with reports on covalent interaction of 5‐caffeoylquinic acid and other quinones with proteins (Ali et al., ; Cao & Xiong, ; Kroll, Rawel, & Rohn, ).…”

“…. findings are in agreement with reports on covalent interaction of 5-caffeoylquinic acid and other quinones with proteins (Ali et al, 2013;Cao & Xiong, 2017;Kroll, Rawel, & Rohn, 2003). In contrast to the alkaline modification, the enzymatic modification primarily affects the free amine groups, whereas a reaction with the thiol group was not observed.…”

“…The observed results of a stronger phenolic binding to WPI at alkaline pH value than with PPO are in line with the observed higher loss of Trp fluorescence after alkaline modification compared to enzymatic treatment (Figure 1A and B) and also the observed stronger covalent modification of amine and thiol groups by RosA at alkaline conditions compared to only an amine group modification after enzymatic treatment (Table 1). In addition, recent studies confirmed that phenolic compounds could already covalently interact with thiol groups at pH 7 (Cao & Xiong, 2017).…”

“…In addition, they are also one of the most popular natural antioxidant sources in food industry, as they are label free (clean label); (Xie et al 2017). As discussed previously, phenolic compounds can interact with proteins and these protein-phenol interactions are likely to alter the physiochemical and functional properties of proteins such as the antioxidant activity and surface hydrophobicity, which opens new opportunities for functional ingredients (Ali et al, 2013;Cao & Xiong, 2017;Cao, Xiong, Cao, & True, 2018;Gan et al, 2016;Jia et al, 2016).…”

Development of Phyllanthus emblica (L) fruit as a carrier for EGCG: Interaction and in vitro digestion study

“…The previous study on the in vitro digestion behavior of EGCG demonstrated that the fluids containing gastrointestinal digestion enzymes accelerated the degradation of EGCG, although this influence was negligible in comparison to that of pH on EGCG (Wu, Sanguansri, & Augustin, ). Food or plant‐derived biomaterials have been used as carriers for EGCG to improve its stability and bioavailability, such as whey proteins, liposome, chitosan, and rice bran proteins (Bhushani, Karthik, & Anandharamakrishnan, ; Cao & Xiong, ; Chung et al, ; Shi et al, ; Ye & Augustin, ).…”